Nanotubes surface

Such carbonyls may be further oxidized using potassium permanganate (KMnO and perchloric acid (HCIO4) to convert all of these groups into carboxylic acids. Once functionalized in this manner, the nanotubes can be fully dispersed in aqueous systems. Kordas et al. (2006) used these derivatives to print nanotube patterns on paper or polymer surfaces to create conductive patterns for potential use in electronic circuitry. The carboxylates also may be used as conjugation sites to link other ligands or proteins to the nanotube surface using a carbodiimide reaction as previously discussed (Section 1, this chapter Chapter 2, Section 1.11 Chapter 3, Section 1). 

Detergents have been used for simple solubilization of SWNTs in aqueous solution. Ionic detergents such as SDS will coat the nanotube surface and expose the negatively charged sulfonate groups to the surrounding aqueous environment, thus allowing SWNT dispersion in aqueous... 

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

Figure 15.16 Some modification methods that are useful for fullerenes also can be used with carbon nanotubes. The reaction of an N-glycine compound with an aldehyde derivative can result in cycloaddition products, which create pyrrolidine modifications on the nanotube surface.

Hepplestone SP, Ciavarella AM, Janke C, Srivastava GP (2006) Size and temperature dependence of the specific heat capacity of carbon nanotubes. Surface Science 600 3633-3636. 

I. Gerber, M. Oubenali, R. Bacsa, J. Durand, A. Gonsalves, M. F. R. Pereira, F. Jolibois, L. Perrin, R. Poteau, P. Serp, Theoretical and experimental studies on the carbon-nanotube surface oxidation by nitric acid Interplay between functionalization and vacancy enlargement, Chem. Eur. J., vol. 17, pp. 11467-11477, 2011. 

K.A. Wepasnick, B.A. Smith, J.L. Bitter, D.H. Fairbrother, Chemical and structural characterization of carbon nanotube surfaces, Analytical and Bioanalytical Chemistry, vol. 396, pp. 1003-1014, 2010. 

Peng, X. and S.S. Wong, Functional covalent chemistry of carbon nanotube surfaces. Advanced Materials, 2009. 21(6) p. 625-642. 

Irantzu, L., et ah, Carbon nanotube surface modification with polyelectrolyte brushes endowed with quantum dots and metal oxide nanoparticles through in situ synthesis. Nanotechnology, 2010. 21(5) p. 055605. 

Polypropylene was grafted onto a nanotube surface using benzoyl peroxide and is discussed by Khabashesku et al. (4). 

Sensor fabrication occurs in two steps. The first step is the immobilization of GOx on the surface of the nanotube. This is accomplished by adding GOx to a solution of surfactant stabilized nanotubes and dialyzing away the surfactant. Dialysis is an ideal method for assembling enzymes on a nanotube surface, because the method allows retention of enzyme activity while simultaneously maintaining nanotube colloidal stability. The resulting GOx-S WNT solution exhibits a shift in the nanotube fluorescence indicative of the enzyme layer being less tightly packed around the nanotube than the surfactant layer. The second step is addition of ferricyanide to the GOx-SWNT solution. Adsorption of ferricyanide to the nanotube surface... 

Figure 11.2 Schematic of GOx-SWNT-based glucose sensor. Glucose oxidase immobilized on the nanotube surface catalyzes the oxidation of glucose. The reaction by-product, hydrogen peroxide, then reacts with the reaction mediator, potassium ferricyanide, adsorbed to the nanotube surface resulting in an increase in SWNT fluorescence. Adapted with permission from Ref. 28.

As nanotubes are inherently hydrophobic and dextran is a very hydrophilic polymer, it is first necessary to functionalize the dextran with hydrophobic phenoxy moieties.29,30 Increasing the weight percent phenoxy content from 0 to 8 wt% results in the increase of the number of nanotube in solution, where dextran alone is not capable of suspending nanotubes in solution. Again, a gentle dialysis method is used to assemble dextran on the nanotube surface. 

In many cases the potential application of single-walled carbon nanotubes is associated with solubility of this nanomaterial in different solvents. Unfortunately, nanotubes are poorly soluble in the most of organic solvents and are insoluble in water, and this fact especially hinders biological using SWNT. Weak solubility of SWNT is a result of substantial van der Waals attractions between nanotubes aggregated in bundles. To solve nanotubes in water without any covalent functionalization, a surfactant would be added into aqueous solution, and then this mixture is suspended by sonication. It is supposed that the sound wave splits bundles in aqueous solution. A surfactant in suspension adsorbed onto the nanotube surfaces precludes aggregation of nanotubes in bundles. 

Scheme 6.2 Covalent reactions targeting carboxylic acids (derived from nanotube surface defects).

Scheme 6.2). For some functional groups such as amines, the covalent amidation functionalization is likely accompanied by significant noncovalent interactions or strong adsorption of the functional groups on the nanotube surface, thus substantially improving some properties of the functionalized nanotube samples (such as excellent water solubility for a hydrophilic functionalization agent16).

Dieckmann et al. in 2003 described an amphiphilic a-helical peptide specifically designed to coat and solubilize CNTs and to control the assembly of the peptide-coated nanotubes into macromolecular structures through peptide-peptide interactions between adjacent peptide-wrapped nanotubes [227]. They claimed that the peptide folds into an amphiphilic a-helix in the presence of carbon nanotubes and disperses them in aqueous solution by noncovalent interactions with the nanotube surface. EM and polarized Raman studies revealed that the peptide-coated nanotubes assemble into fibers with the nanotubes aligned along the fiber axis. The size and morphology of the fibers could be controlled by manipulating the solution conditions that affect peptide-peptide interactions [227]. 

Though not strictly functioning as resistors/conductors, carbon nanotubes have just been reported in an extraordinarily vapor-sensitive capacitive device [19]. The electric field lines emanating from the nanotubes are responsible for a localized dielectric response that can be modulated by minute quantities of adsorbate on the nanotube surface. A layer of hydrogen-bonding polymer, or even a mono-layer terminated in mildly acidic groups, increased sensitivity to parts per billion levels. Response strength was correlated with the dipole moment of the analytes. 

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